When higher efficiency, smaller size, lighter weight, and prolonging battery lifetime are required, switching regulators are used for power management as replacements for simpler linear regulators. Furthermore, while the linear regulators can only step down, the switching regulators can be configured to step up (boost), step down (buck), or invert the output voltage with respect to the input voltage. A switching regulator is basically a circuit for regulating the voltage across a load. It transfers energy from input to output in discrete packets and a feedback circuitry regulates the energy transfer to maintain a constant voltage within the load limits of the circuit. Portable devices often operate in low-power stand-by mode because increasing the efficiency significantly increases the battery life.
The popular control scheme for switching regulators is the pulse-width modulation (PWM). The control uses a constant switching frequency but varies the duty cycle as the load current varies. This scheme achieves good regulation, low noise spectrum, and high efficiency; however, when the load current is low the PWM mode is not efficient due to the switching loss and the high quiescent current.